1. Field of the Invention
This invention relates to automatic lockout mechanisms for electrical equipment containers.
2. Description of the Related Art
Electrical equipment such as circuit breakers is typically housed within containers designed to prohibit access to the equipment at times when servicing the equipment would be unsafe. A circuit breaker for medium voltage applications will typically include male and female connectors for disconnecting the circuit breaker from the circuit prior to opening the circuit breaker""s container. Additionally, it is generally considered desirable to house such circuit breakers within an arc resistant container. To qualify as arc resistant, the door of the container must remain closed while the circuit breaker is in operation.
One example of a system for preventing access to a fuse box while the fuses are connected to the circuit is described in U.S. Pat. No. 5,757,260, issued to J. E. Smith et al. on May 26, 1998. This patent describes a pivoting rod blocking rotation of the door""s handle when the box containing the fuses is not fully retracted from the circuit. When the box if fully retracted, a pin on the carriage roller engages a camming surface on the rod, disengaging the rod from the door handle mechanism and permitting the door to be opened. Additionally, a slider prevents access to the threaded rod of the levering in mechanism when the door""s handle is rotated away from the locked position, thereby securing the carriage in the retracted position. An interlock acting on the door itself may be more reliable than an interlock acting on the door handle.
U.S. Pat. No. 5,905,244, issued to J. E. Smith et al. on May 18, 1999, describes an arc-resistant metal-clad switchgear. When the doors of the cabinet are closed, a plurality of tabs on the doors are positioned behind corresponding tabs on the edges of the cabinet""s doorframe, thereby helping the door resist an explosion inside the cabinet.
U.S. Pat. No. 6,066,814, issued to J. E. Smith et al. on May 23, 2000, describes an interlock for a cabinet containing electrical equipment. The interlock includes a key actuated slider for securing a source breaker in a test position. The key necessary for accessing the levering in mechanism for the other breakers is secured within the lock of the source breaker unless the source breaker is locked in this test position, thereby cutting off current to the other breakers.
Therefore, there is a need for an improved interlock for electrical cabinets wherein the interlock mechanism secures the door itself, instead of the door""s operating handle. Additionally, there is a need for an improved interlock having fewer components, greater reliability, and easier manufacture than previous interlocks.
The present invention is an automatically operating interlock for electrical cabinets, such as arc resistant circuit breaker cabinets. The interlock prevents opening the cabinet door unless the circuit breaker is completely disconnected from the circuit.
A typical circuit breaker for medium voltage applications is mounted on a carriage that is movable between a forward, disengaged position and a rearward, engaged position within the cabinet containing the circuit breaker. At least one pair of quick disconnects terminating in finger clusters protrudes from the rear of the circuit breaker, being dimensioned and configured to engage a pair of stabs at the rear of the circuit breaker""s cabinet when the circuit breaker is in the rearward position, thereby connecting the circuit breaker to the protected circuit. A typical medium voltage circuit breaker will use three pairs of mating stab/quick disconnect combinations. When the circuit breaker is moved to its forward position, the finger clusters are withdrawn from the quick disconnects, thereby disconnecting the circuit breaker from the circuit.
Moving the circuit breaker from one position to the other is accomplished by means of a threaded rod extending from the front to the rear of the cabinet. A levering in block engages the threaded rod so that rotation of the threaded rod pushes the levering in block either forward or rearward. The levering in block is secured to the carriage, so that rotation of the threaded rod thereby moves the carriage forward or backward. This process is known as levering in.
The interlock includes a locking bar pivotally secured to a cam at one end and selectively engaging the cabinet""s door at the other end. The cam is pivotally secured adjacent to the levering in apparatus, and is spring biased to hold the locking bar against a locking tab within the door. When the levering in block reaches its forwardmost position, it contacts the cam, rotating the cam so that the locking bar is retracted from the door. The door may thereby be opened. Moving the levering in block rearward permits the cam to rotate the locking bar back into engagement with the cabinet door.
It is therefore an aspect of the present invention to provide an automatically operating interlock for preventing access to electrical cabinets when the electrical equipment therein is connected to a power supply.
It is a further aspect of the present invention to provide an automatic interlock for electrical cabinets having a locking bar dimensioned and configured to secure a door in its closed position, and a cam dimensioned and configured to retract the locking bar from the door on the electrical equipment within the cabinet is disconnected.
It is an additional aspect of the present invention to provide an automatic interlock for electrical cabinets, preventing access to the interior of the cabinet whenever the levering in assembly therein is in any position except its forwardmost position.
It is a further aspect of the present invention to provide an automatically operating interlock directly engaging the door of the cabinet, thereby preventing the door of the cabinet from being raised prior to being rotated to its open position.
It is an additional object of the present invention to provide an automatic interlock for electrical cabinets that is simpler, more reliable, and easier to manufacture than previously available interlocks.
These and other aspects of the invention will become apparent through the following description and drawings.